Retinol formulations and methods for their use

ABSTRACT

A composition for the treatment of skin comprises a non-emulsified, aqueous suspension of retinol. The composition may further include at least one protein species, and some proteins used in the composition include collagen and elastin. The composition may also include hyaluronic acid. The composition may also include one or more of tocopheryl acetate, propylene glycol, and linseed extract. Also disclosed are methods for making the composition and use of the composition for the treatment of skin.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of U.S. Provisional Patent Application Ser. No. 61/111,819 filed Nov. 6, 2008, entitled “Retinol Formulations and Methods for Their Use” which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to formulations and methods for the treatment of skin. More particularly the invention relates to formulations and methods wherein the active ingredient is a retinol. Most specifically the invention relates to formulations and methods based upon non-emulsified compositions of retinol wherein retinol is suspended in an aqueous vehicle.

BACKGROUND OF THE INVENTION

Retinoic acid is a very effective agent for the treatment of a variety of skin conditions including, but not limited to, acne, photo aging, wrinkles, and the like. One particular retinoic acid material used for skin treatment is tretinoin (all-trans retinoic acid). While retinoic acid is a highly effective therapeutic material, it can cause a number of undesirable side effects which include skin irritation and skin thinning among others. As a consequence, topical formulations comprising retinoic acid must be used with caution, and dosage control is critical. In order to avoid adverse side effects, retinoic acid therapies often rely upon the use of topical preparations of retinoic acid precursors and derivatives.

Retinal is a member of the vitamin A family and can be converted to retinoic acid under oxidizing conditions. As is known in the art, when retinol is applied to the skin, it can bioconvert to retinoic acid, and this conversion reaction is fostered by the presence of proteins. For this reason, retinol based preparations are attractive for use as therapeutic agents for the treatment of a variety of skin conditions since they can act, controllably, to deliver retinoic acid to the skin. However, retinol is a fat-soluble material and has very low solubility in aqueous vehicles. This solubility problem has limited the use of retinol based formulations.

In some instances, in order to overcome the disadvantages of using an oil based therapeutic material, emulsified preparations of retinol have been prepared. As is understood in the art, an emulsified formulation comprises a microstructure having an oily phase disposed in a continuous, aqueous phase (oil in water emulsion) or an aqueous phase disposed in an oily, continuous phase (water in oil emulsion). In an emulsion, the first phase may be present in the form of discrete vesicles or in layered (lamellar) structures which are disposed in the continuous phases. In the context of this disclosure, all of such dual phase formulations are understood to be emulsions. A typical emulsion requires the presence of an emulsifying agent in order to prevent the phases from separating and thereby destroying the emulsion. The emulsifying agent comprises a molecule having an oleophilic portion which binds to the material comprising the oily phase and a hydrophilic portion which binds to the aqueous phase.

While emulsified preparations of retinol are known, it has been found that emulsified preparations of retinal have decreased efficacy when used as topical agents for the treatment of skin. This is because the emulsified structure inhibits the absorption of retinol by the skin and its subsequent bioconversion to the active, retinoic acid form. As a consequence, retinol based skin treatment formulations have been found to have limited utility, and hence the more risky retinoic acid based formulations are often used instead. As will be explained hereinbelow, the present invention provides aqueous-based, non-emulsified retinal preparations which are highly effective in treating various skin conditions.

BRIEF DESCRIPTION OF THE INVENTION

Disclosed is a composition for the treatment of skin, which comprises a non-emulsified, aqueous suspension of retinol. The composition may further include at least one protein species, and some proteins which may be employed in the invention include collagen and elastin. The composition may include further ingredients such as hyaluronic acid as well as adjunct agents including thickeners, fragrances, coloring agents, preservatives, and buffers.

Specific compositions include, on a weight basis, 0.1-5.0% retinol and 1-20% of at least one protein species, together with water and at least one dispersing agent which operates to suspend the retinol. The composition is characterized in that it is not an emulsion and the retinol is suspended in the water. In specific instances, the retinol is in the form of a plurality of droplets which have a size in the range of 5-500 microns.

Another specific composition comprises, on a weight basis, 0.1-5% retinol, 1-15% soluble collagen, 0.5-5% hydrolyzed elastin, 0.2-2% hyaluronic acid, 0.5-10% glycerin, one or more dispersing agents and water. Also disclosed are other compositions as well as methods for preparing and using the compositions.

DETAILED DESCRIPTION OF THE INVENTION

The present invention recognizes that retinal can be a highly effective agent for the treatment of skin when it is applied thereto in a non-emulsified vehicle. Specifically, the present invention recognizes that retinol may be compounded into a suspension of fine droplets which are dispersed in an aqueous vehicle, and that this suspension will have enhanced utility as compared to emulsified preparations. This finding is counterintuitive and unexpected. Emulsified compositions are easy to prepare, and are considered in the art to be the optimum vehicle for delivering retinol to the skin. Suspensions are much more difficult to prepare than are emulsions. Furthermore, the prior art had no reason to expect that suspensions of retinol would be any more effective than emulsions as a topical treatment for skin. Hence, the prior art has never considered or employed suspensions of retinol for the treatment of skin conditions, and has not anticipated the enhanced therapeutic effect of the suspensions of the present invention.

In accord with the present invention it has been found that a composition for the treatment of skin comprising a non-emulsified, aqueous suspension of a retinal is highly effective in the topical treatment of a variety of skin conditions. In the art, the term “retinol” is used broadly to refer to a family of materials of the general formula C₂₀H₃₀O having a terminal hydroxyl group. The term “retinol” also is used to refer to esters and other derivatives of this alcohol since these materials are often found in the biological systems as precursors of retinal. In the context of this disclosure, the term “retinol” is understood to include all of such materials.

The materials of the present invention are specifically characterized in that the compositions do not comprise any type of emulsified structure. As such, they do not include any material which is operative, in the formulation, to bind to an oily phase material and to an aqueous phase material so as to form a vesicular or lamellar emulsion structure. It is to be understood that compositions of the present invention may include materials which can function as emulsifiers in other systems, provided that those materials are not operative in the present formulations to form or sustain any emulsion. The compositions of the present invention can include dispersants or other suspension promoting agents which, through electrostatic action, rheological control, or some other mechanism, maintain the retinal in suspension. As detailed above, the suspensions of the present invention are differentiated from emulsions by the lack of an emulsifying agent which binds to the retinal and to the aqueous phase. This distinction is significant since it is believed to be responsible for the fact that the suspensions of the present invention have a greater therapeutic effect than do comparable emulsified preparations.

The compositions of the present invention may further include other performance ingredients. In one particular group of instances, the formulations include one or more proteins therein, and it has been found that inclusion of a protein can enhance the bioconversion of the retinol to retinoic acid. Typically, the proteins are present in a solubilized form. Some of the proteins which may be included in the formulations of the present invention include soluble collagen and hydrolyzed elastin. The compositions may also include other performance ingredients such as hyaluronic acid. The compositions may also include ancillary ingredients as is known in the art and these may include thickeners, fragrances, coloring agents, preservatives, buffers, and the like.

The amount of retinal present in the composition will depend upon particular applications. In some instances, it has been found that the concentration of the retinal will be in the range of 0.1-5.0%. This concentration is given on the basis of weight, and unless otherwise noted, all concentrations given herein are on a weight/weight basis. In those instances where proteins are incorporated, they will typically be present in an amount of 1-20%; although, higher or lower concentrations are also contemplated. Hyaluronic acid, when it is included, is typically present in a concentration of 0.1-5%.

One particular group of compositions of the present invention may be formulated as an aqueous dispersion which includes at least the following performance materials:

-   -   0.1-5% retinol;     -   1-15% soluble collagen;     -   0.5-5% hydrolyzed elastin;     -   0.2-2% hyaluronic acid; and     -   0.5-10% glycerin.

The foregoing composition may also include additional agents, and in one particular group of instances, the composition further includes:

-   -   0.5-5% propylene glycol;     -   0.1-2% tocopheryl acetate;     -   0.5-5% Linum usitatissimum (linseed) seed extract;     -   0.5-5% magnesium aluminum silicate;     -   0.1-3% octoxynol-9;     -   0.1-2% quaternium-15;     -   0.1-5% polysorbate 20; and     -   0.1-2% xanthan gum.

One particular composition of the present invention comprises:

-   -   magnesium aluminum silicate 0.99%;     -   soluble collagen 8.00%;     -   hydrolyzed elastin 2.00%;     -   hyaluronic acid 1.00%;     -   Linum usitatissimum (linseed) seed extract 0.98%;     -   retinol 1.00%;     -   tocopheryl acetate 0.50%;     -   octoxynol-9 0.80%;     -   quaternium-15 0.30%;     -   propylene glycol 0.90%;     -   glycerin 3.00%;     -   polysorbate 20 1.00%;     -   xanthan gum 0.50%; and     -   balance water.

In another group of formulations, the retinol component is employed in the form of a pre-blended, 50/50 mixture of retinol and polysorbate 20. This is for convenience and it is to be understood that the pre-blended mixture need not be employed. One formulation of this type comprises:

-   -   magnesium aluminum silicate 0.99%;     -   soluble collagen 8.00%;     -   hydrolyzed elastin 2.00%;     -   sodium hyaluronate 1.00%;     -   Linum usitatissimum (linseed) seed extract 0.98%;     -   retinol/polysorbate (50/50 mixture) 1.00%;     -   tocopheryl acetate 0.50%;     -   octoxynol-9 0.80%;     -   quaternium-15 0.30%;     -   propylene glycol 0.90%;     -   glycerin 3.00%;     -   xanthan gum 0.50%;     -   Yellow No. 5 (1% solution) 0.12%; and     -   water balance.         A second formulation of this type comprises:     -   magnesium aluminum silicate 0.99%;     -   soluble collagen 8.00%;     -   hydrolyzed elastin 2.00%;     -   sodium hyaluronate 1.00%;     -   Linum usitatissimum (linseed) seed extract 0.98%;     -   retinol/polysorbate (50/50 mixture) 2.00%;     -   tocopheryl acetate 0.50%;     -   octoxynol-9 0.80%;     -   polysorbate 20 2.50%;     -   quaternium-15 0.30%;     -   propylene glycol 0.90%;     -   glycerin 3.00%;     -   xanthan gum 0.50%;     -   Yellow No. 5 (1% solution) 0.22%; and     -   water balance.

The foregoing formulations may be readily prepared by dispersing liquid retinol, and the other components into the aqueous vehicle. Dispersion may be facilitated by the use of a blender, mill or the like. In some instances, the particle or droplet size of the retinol is in the range of 5 microns-500 microns; although, other sizes may be utilized in particular formulations.

In a typical therapeutic protocol, the composition is applied to the skin one or two times a day; although other application schedules may be employed in particular instances.

The foregoing is descriptive of sonic particular embodiments and implementations of the present invention and is meant to be illustrative of the general principles thereof, and not a limitation upon the practice of the invention. Other modifications and variations will be readily apparent to those of skill in the art in view of the teaching presented herein. It is the following claims, including all equivalents, which define the scope of the invention. 

1. A composition for the treatment of skin, said composition comprising: a non-emulsified, aqueous suspension of retinol.
 2. The composition of claim 1, further including at least one protein species.
 3. The composition of claim 2, wherein said at least one protein species is selected from the group consisting of: collagen, elastin, and combinations thereof.
 4. The composition of claim 1, further including hyaluronic acid.
 5. The composition of claim 1, further including an ancillary ingredient selected from the group consisting of: thickeners, fragrances, coloring agents, preservatives, buffers, and combinations thereof.
 6. A composition for the treatment of skin, said composition comprising, on a weight basis: 0.1-5.0% retinol; 1-20% of at least one protein species; and water, said composition characterized in that it is not an emulsion, and said retinol is suspended in said water.
 7. The composition of claim 6, wherein said retinol is in the form of droplets having a size in the range of 5-500 microns.
 8. The composition of claim 6, further including 0.1-5% by weight of hyaluronic acid.
 9. A composition for the treatment of skin, said composition comprising, on a weight basis: 0.1-5% retinol; 1-15% soluble collagen; 0.5-5% hydrolyzed elastin; 0.2-2% hyaluronic acid; 0.5-10% glycerin; and the remainder water.
 10. The composition of claim 9, further including, on a weight basis, at least one of 0.5-5% propylene glycol; 0.1-2% tocopheryl acetate; 0.5-5% Linum usitatissimum (linseed) seed extract; 0.5-5% magnesium aluminum silicate; 0.1-3% octoxynol-9; 0.1-2% quaternium-15; 0.1-5% polysorbate 20; and 0.1-2% xanthan gum.
 11. The composition of claim 9, further characterized in that said composition is not an emulsion.
 12. A composition for the treatment of skin, said composition comprising, on a weight basis: 0.99% magnesium aluminum silicate; 8.00% soluble collagen; 2.00% hydrolyzed elastin; 1.00% sodium hyaluronate; 0.98% Linum usitatissimum (linseed) seed extract; 1.00% retinol/polysorbate 20 (50/50 mixture); 0.50% tocopheryl acetate; 0.80% octoxynol-9; 0.30% quaternium-15; 0.90% propylene glycol; 3.00% glycerin; 0.50% xanthan gum; and the balance water.
 13. The composition of claim 12, further including one or more ancillary agent selected from the group consisting of: coloring agents, fragrances, thickening agents, buffers, and preservatives.
 14. A composition for the treatment of skin, said composition comprising, on a weight basis: 0.99% magnesium aluminum silicate; 8.00% soluble collagen; 2.00% hydrolyzed elastin; 1.00% sodium hyaluronate; 0.98% Linum usitatissimum (linseed) seed extract; 2.00% retinol/polysorbate 20 (50/50 mixture); 0.50% tocopheryl acetate; 0.80% octoxynol-9; 2.50% polysorbate 20; 0.30% quaternium-15; 0.90% propylene glycol; 3.00% glycerin; 0.50% xanthan gum; and the balance water.
 15. The composition of claim 14, further including one or more ancillary agent selected from the group consisting of: coloring agents, fragrances, thickening agents, buffers, and preservatives.
 16. A method for the treatment of skin, said method comprising applying to the skin a composition comprising, on a weight basis: 0.1-5.0% retinol; 1-20% of at least one protein species; and the remainder water; wherein said composition is characterized in that it is not an emulsion, and said retinol is suspended in water. 